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P. PROFOS 3,125,073 TER METHOD AND APPARATUS FOR CONTROLLING FEEDWASUPPLY TO A FORCED FLOW STEAM GENERATOR Filed D80. 23, 1960 5Sheets-Sheet 1 gig 9.35%? 93 539:": 3.2% Qcmtofim E EQQE @9896" m 3.2% mweoqm 3385382 EE xuE 18 8.5% 25:86 S ERE .635 int "E v 3.3% R aE 2:55 343.8393 EQQ T E SQEQu 33393 uc t equm 5 2.: motutcm ou t3 um m mt March17, 1964 P. PROFOS 3,125,073

METHOD AND APPARATUS FOR CONTROLLING FEEDWATER SUPPLY TO A FORCED FLOWSTEAM GENERATOR Filed Dec. 23, 1960 5 Sheets-Sheet 2 I T I, h 2 1 Iii F(9- 6 b, I J

1,0 T 140 0,8 k E Q q g 06 1a0 Q Q F u 2 i E Q 04 I 2 3 o d I: 02 k 540wDom/NZ T be h F /g. 5

C2 jm errtorz' March 17, 1964 P. PROFOS 3,125,073

METHOD AND APPARATUS FOR CONTROLLING FEEDWATER SUPPLY TO A FORCED FLOWSTEAM GENERATOR Filed Dec. 23, 1960 5 Sheets-Sheet 3 AOAUO W? v v 4 v Aa. A

March 17, 1964 P. PRO METHOD AND APPARATUS FOR CONTROLLING 'FEEDWATERSUPPLY TO A FORCED FLOW STEAM GENERATOR Filed Dec. 23, 1960 5Sheets-Sheet 4 Inventor! Pquz. PPOFOS.

March 17, 1964 P. PRoFos 3,125,073

METHOD AND APPARATUS FOR CONTROLLING'FEEDWATER SUPPLY To A FORCED FLOWSTEAM GENERATOR Filed Dec. 23, 1960 5 Sheets-Sheet 5 .fm eman' PAUL Poros.

United States Patent METHGD AND APPARATUS FGR CONTROLLING FEEDWATERSUPPLY TO A FORCED FLOW STEAM GENERATOR Paul Protos, Winterthur,Switzerland, assignor to Sulzer Freres, S.A., Winterthur, Switzerland, acorporation of Switzerland Filed Dec. 23, 1960, Ser. No. 78,004 Claimspriority, application Switzerland Dec. 31, 1959 Claims. (Cl. 122379) Thepresent invention relates to a method and an apparatus for controllingthe feedwater supply to a forced flow steam generator having anevaporating section and a superheating section and a water separatorinterposed between said sections.

It is known to provide water separators in forced flow steam generatorsand to control the feedwater supply so that a mixture of steam andliquid leaves the evaporating section of the steam generator. The liquidphase of the operating medium is separated in the water separator fromthe steam phase and is blown down. In this way salts which enter thesteam generator with the feedwater, are removed from the generatortogether with the blowdown water so that the salts Will not enter thesuperheater section or sections.

Blowing down of liquid operating medium containing salts is accompaniedby a loss of heat energy and of operating medium, and severalarrangements have been proposed to reduce this loss. With moderndesalting plants continuous blowdown and losses caused thereby can benearly completely avoided and blowing down of a relatively great amountof liquid operating medium is only necessary when the salt content ofthe operating medium flowing. through the steam generator increasesabove a permissible value, for example, due to leakage in a condenser orbreak-through of an ion exchanger.

It is an object of the present invention to provide a method andapparatus whereby the amount of blowdown water in a forced flow steamgenerating plant in which a water separator is interposed between anevaporating part and a superheating part is reduced to a minimum bycontrolling the rate of supply of feedwater to the steam generator inresponse to the salt content of the operating medium of the plantwhereby the rate of feedwater supply to the steam generator is increasedupon an increase of the salt content above a predetermined value and therate of feedwater supply is decreased when the salt concentration dropsbelow a predetermined value.

In a further development of the invention the control of the rate offeedwater supply to the steam generator in response to the salt contentof the operating medium is combined with a control of the feedwatersupply in response to values representing certain operating conditionsof the plant, such as load on or steam output of the steam generator,temperature of the operating medium passing through the steam generator,and the like.

The apparatus according to the invention'includes a regulator forregulating the rate of feedwater supply and means for adjusting the setpoint of the regulator. The set point adjusting means is primarilyactuated by control signals produced by conventional devices which areresponsive to operating conditions of the steam generator and effect anincrease of the rate of feedwater supply, for example, if the steamdemand on the generator rises and/ or if the temperature of theoperating medium passing through the steam generator rises above apredetermined limit, and vice versa. According to the invention aswitching device is provided in signal transmitting means between thesignal producing devices and the feedwater regulator. This switchingdevice is actuated in response to the salt content of the operatingmedium for 3,125,073 Patented Mar. 17., 1964 setting the device totransmit a signal corresponding to a relatively high set point of thefeedwater regulator and effecting an increased rate of feedwater supplywhen the salt concentration is high and for switching the device totransmit a set point control signal which effects a reduced rate offeedwater supply when the salt concentration drops below a predeterminedvalue, and vice versa.

The aforesaid switching device may include means for holding theswitching device in a position for transmitting the lower set pointsignals as long as the salt concentration is below a certain upper limitand for changing, preferably at constant speed, the position of theswitching device to a position for transmitting the higher set pointsignals when the salt concentration reaches said limit and for holdingthe switching device in the last mentioned position until the saltconcentration reaches a predetermined lower limit whereupon theswitching device is moved, preferably at constant speed, to the positionfor transmitting the lower set point signals to the feedwater regulator.

In a modification of the invention a by-pass pipe containing a valve isprovided for by-passing the water separator and said valve is controlledin response to the salt content of the operating medium for opening thevalve upon a drop of the salt content below a predetermined value andclosing the valve according to an increase of the salt content.

The novel features which are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, and additional objects and advantages thereof will bestbe understood from the following description of embodiments thereof whenread in connection with the accompanying drawing wherein:

FIG. 1 is a schematic illustration of a forced fiow steam generatingplant embodying an automatic control according to the invention.

FIG. 2 is a diagram showing the removal of Si0 by blowdown from theoperating medium of a plant as shown in FIG. 1 at different blowdownrates and operating pressures.

FIG. 3 is a diagrammatic illustration of a mechanism forming part of theplant shown in FIG. 1.

FIG. 4 is a diagrammatic part sectional illustration of a modificationof the mechanism shown in FIG. 3.

FIGS. 5 and 6 are diagrams illustrating the relation between the rate ofsupply of operating medium to the steam generator and different saltcontents of the operating medium.

FIGS. 7 and 8 are diagrammatic illustrations of forced flow steamgenerating plants embodying two modifications of an automatic controlaccording to the invention.

FIGURE 9 is a key to the letter symbols used in the drawings.

FIG. 1 illustrates, by Way of example, a simple embodiment of theinvention. The operating medium, namely feedwater, is supplied by a feedpump 1 through a valve 2 and an orifice plate 3 to an evaporatingsection 4 of a steam generator. The evaporating section 4 comprises aplurality of tube lines arranged in parallel relation with respect tothe fiow of the operating medium therethrough. At the end of each tubeline a temperature sensitive device 5 is provided. The operating mediumis discharged from the tube lines into a collector 6 wherefrom theoperating medium is conducted into a water separator 7. The steam phaseof the operating medium is conducted from the separator 7 to asuperheater 8. The superheated steam operates a turbine 9 whose exhaustis condensed in a condenser 10. The condensate is pumped by a pump 11into a feedwater tank 12 from which the feed pump 1 receives feedwater.The blowdown water from the separator '7 is cooled in a cooler 27,purified in a purifier 28, for example, of the ion exchange type andreturned to the circuit upstream of pump 11. If needed, raw water may besupplied to the circuit through a valve 29 andthe purifier 28. a a

The valve 2 is controlled by a regulator 13 which is responsive to therate of flow of feedwater into the evaporating section 4, a rate of flowmeasuring device 14 including the measuring orifice plate 3 beingprovided for this purpose. The set point of the regulator 13, i.e. thedesired rate of flow to be effected by the valve 2, is defined by adevice 15. The latter is actuated by that one of the temperaturesensitive devices 5 which senses the highest temperature. A systemsuitable for this purpose is disclosed in Patent No. 2,800,887. Alldevices 5 which sense a lower temperature at the same time areineffective on the device 15. Rising of said highest temperature above apredetermined value causes an increase of the set point of the regulator13, i.e., opening of valve 2 and increased feedwater supply to the steamgenerator and vice versa. The object of the control apparatus is toassure that slightly superheated steam leaves the tube line of theevaporator 4 producing the relatively highest temperature of theoperating medium and all other tube lines of the evaporator 4 produce alower temperature of the operating medium which contains a certainpercentage of unevaporated operating medium. This unevaporated portionis separated in the separator 7 and is blown down through a valve 16which is controlled in the conventional manner by a regulator 17 inresponse to the water level in the separator. Forced flow steamgenerators are provided with means for maintaining a desired steampressure in the generator. These means are not shown because they areconventional and complicated and do not form part of the presentinvention.

The set point of the control device which produces the set point of theregulator 13 also corresponds to a signal supplied to the device 15through a conduit 20 which is connected by aswitching device 21 eitherto a signal conduit 22 or to a signal conduit 23. The signals conductedby the conduits 22 and 23 are different and correspond to difierentloads on and steam output of the steam generator. The signals areproduced by a load control device 24 controlling the operation of thesteam generator in a conventional manner by controlling the set pointsof conventional regulators, not shown, for example, of the rate of fueland rate of combustion air supply to the steam generator. An apparatusof this type is shown in Patent No. 2,962,865. Relatively low set pointsetting signals are conducted through the conduit 23 and relatively highset point setting signals are conducted through the conduit 22. At asuitable point 25 of the circuit of the operating medium through theplant a device 26 is connected which produces control signalscorresponding to the salt concentration in the operating medium at thispoint. The signals produced in the device 26 actuate the switchingdevice 21.

If the salt concentration of the operating medium circulating throughthe plant is at or below a predetermined concentration, the switchingdevice 21 connects the de vice 15 to the signal conduit 22 whichproduces a higher temperature set point for the device 15 so that thelatter, through the device 13 and the valve 2, effects a reduced rate ofsupply of feedwater to the steam generator. If the salt concentrationincreases above a predetermined value for any reason, for example, dueto malfunction of a desalting plant, the concentration sensing device26- actuates the switching device 21 to connect the conduit 23 to thedevice 15 whereby the temperature set point of the device 15 is reducedand the rate of feedwater supply is increased. Since now more operatingmedium is fed into the evaporating section 4, the operating mediumleaving the evaporating section contains a greater portion ofunevaporated liquid which is separated in the separator 7 and blown downtherefrom. As soon as the salt concentration of the circulatingoperating medium drops below the predetermined maximum, the device 26actuates the switching device 21 to connect the conduits 22 and 20whereby the temperature set point of the device 15 is increased and therate of flow set point of the device 13 is reduced.

The abscissae of the diagram FIG. 2 represent rate of blowdown from theseparator 7 in percent of rate of flow of feedwater supplied to theevaporating section 4. The ordinates represent the relation between therate of salt removal and the rate of salt passing through theevaporating section. The balance of salt passes with the steam into thesuperheater 8. The curves plotted in the diagram represent the relationbetween the rates of salt removal and of salt passing through theevaporating section at various pressures (atmospheres absolute) atvarious blowndown percentages. The diagram shows that, particularly whenoperating at high pressures, the saltremoving eifect of the separatorincreases upon increase of the blowdown rate to about 15%. It is,therefore, of advantage toincrease the blowdown rate when the saltcontent of the feedwater increases. The line designated by the letter krepresents the situation when operating at the critical pressure. Atthis pressure the amount of salt carried over by a pound of steam intothe superheater is relatively great and the total amount of salt carriedinto the superheater is reduced if less steam is passed into thesuperheater, i.e., if more water is blown down. At a lower steampressure, for example 140 atmospheres, less salt is carried over by apound of steam into the superheater and a reduction of the rate of steampassing into the superheater by increasing the blowdown rate above 15%has little effect on the total salt removal.

FIG. 3 shows a particular form of the switching device 21. The signalproduced by the salt concentration sensitive device 26 acts on a rod 30which is connected to and moves a wiper arm 31 of a potentiometer 32.The ends of the latter are connected to electric conduits 22 and 23which are charged, for example, according to the position of aconventional device which is actuated according to operating conditionsof the plant. Depending on the position of the arm 31, either thevoltage in line 22 or the voltage in line 23, or an intermediate voltageis transmitted to the signal conduit 20 for controlling the set point ofthe device 15.

FIG. 4 shows a modified swtiching device 21. Hydraulic pressure istransmitted to cylinders and 41 through signal conduits 22 and 23,respectively, the pressures acting on spring-loaded pistons 4-2 and 43,respectively. The pistons act through piston rods 44 and 45 on a movableguide 46 whose position is defined by the pistons 42 and 43. A slide 47is movable on the guide 46 and is pivoted to one end of a lever 49 whoseother end is pivoted to one end of an axially movable rod 48. The otherend 51 of the rod 48 is enlarged and is placed opposite the outlet of anair channel 52 in a piston 53 which is connected to a rod 20 whichtransmits signals corresponding to the position of the piston 53 as setpoint defining signals to the device 15. The piston 53 has three partsof different diameters; the largest part is movable in a cylinder and isprovided with a channel 54 extending between the two faces of the largepiston part. Air under pressure is introduced into the cylinder 55through an air inlet 56.

The lever 49 is actuated by a rod 50 which is connected to a piston rod57 extending from a piston 58 in a cylinder 59. A pipe 60 for conductinga pressure fluid is connected to one end of the cylinder 59 and a pipe61, also for conducting a fluid under pressure, is connected to theother end of the cylinder 59. A piston valve 63 in a cylinder 62controls the flow of a fluid under pressure supplied by a pump 64 to andfrom the pipes 60 and 61. Fluid relieved through the valve 63 is removedthrough a pipe 65. The end of a rod connected to the piston valve 63forms an armature 66 adapted to cooperate with coils 67 and 68. v Oneend of each of the coils is connected to one pole of a source ofelectricity 69, the other ends of the coils 67 and 68 are connected tocontacts 70 and 71. These contacts cooperate with a movable contact 72which is actuated by signals produced by the salt concentrationsensitive device 26. The movable contact 72 is arranged in seriesrelation with a second movable contact 73 which is adapted to engageeither one of two stationary contacts 74 and 75 which are both connectedto the second pole of the source 69. The contact 73 is connected by alink 76 to the lever 49 to follow the movements thereof.

If the salt content of the feedwater entering the evaporator 4 is small,the movable contact 72 engages the stationary contact 70 so that thecoil 67 is energized and the armature 66 is moved to the left and placesthe valve 63 in its left end position, as seen in FIG. 4. The space inthe cylinder 59 below the piston 58 is now connected to the pump 64 andthe space above the piston 53 is connected to the outlet pipe 65. Thepiston 58 is in its upper end position and the lever 49 is in theposition shown in FIG. 4. If the salt content of the feedwater increasesabove a predetermined value, the salt concentration sensitive device 26moves the contact 72 to engage the contact 71 whereby the coil 68 isenergized, current flowing through the contacts 73 and 74 which arestill in engagement. The armature 66 is now pulled to the right and thepiston valve 63 placed in its right end position so that the space abovethe cylinder 58 is connected to the pump 64 and the space below thepiston 58 is connected to the outlet pipe 65. The piston 58 now moves ata constant speed which is determined by the output of the pump 62 in adownward direction. This causes downward swinging of the lever 49 anddisengagement of the contacts 73 and 74 which, however, has noinfluence, because the valve 63 remains in the new end position. Thepiston 58 moves at constant speed until it arrives at its lower endposition whereupon the contact '73 engages the contact 75. This,however, has no influence on the position of the piston 58 as long asthe movable contact 72 does not engage the contact 70. This engagementis effected only after reduction of the salt content of the feedwaterand causes movement of the piston valve to the left so that the piston58 moves at constant speed from its lower end position into the upperend position which is shown in FIG. 4. Movement of the piston 58 causesmovement of the slide 47 at the end of the lever 49 along the guide 46so that a signal arriving through the conduit 22 or a signal arrivingthrough the conduit 23, or an intermediate signal is transmitted to therod 48.

The compressed air introduced into the cylinder 55 through the inlet 56passes through the channel 54 and to the right side of the piston 53 andtherefrom through the channel 52 to the outside. The air passing throughthe channel 54 is throttled in a constant manner and is variablythrottled at the outlet of the channel 52 by the end 51 of the rod 48.The piston 53 moves to a position where the pressures at the left sideand at the right side of the piston are the same. The rod 2% connectedto the piston 53 thus follows the movement of the rod 48 withoutexerting undue pressure on the rod 48.

The abscissae in the diagram FIG. 5 represent salt concentration. Theordinates represent the set points of the control for the rate offeedwater supply which set points correspond to the position of thelever 31 in FIG. 3. The heavy line in FIG. 5 represents the set pointsof the control for the rate of feedwater supply when using the apparatusshown in FIG. 3. The lever 31 remains in the position h until the saltconcentration amounts to the value C so that the set point of thecontrol produces a relatively small rate of feedwater supply. If thesalt concentration increases above the concentration C the rate offeedwater supply is also increased and the lever 31 is moved towards theposition h If the salt concentration reaches the value C and increasesabove said value, the lever is in the position h and remains in thisposition so that the rate of feedwater supply is not further increasedthough the salt concentration may increase beyond the value C As isobvious from FIG. 2, when operating at 140 atmospheres and blowing downabout 15% of the operating medium passing through the evaporator, of thesalt contained in the feedwater is removed with the blowdown water andit is of little advantage to blow down more water. Only at very highpressures, close to the critical pressure, an increase of the blowdownrate above 15% of the feedwater supply rate substantially reducespassage of salt into the superheater, because at such high pressures theamount of salt carried along by each pound of steam is much greater thanat lower pressures. Such increase of the blowdown rate, however, causesexcessive losses of energy and operating medium. For this reason it isnot contemplated to increase the blowdown rate above a certain valuewhich depends on the pressure at which the steam generator is operated.

FIG. 6 illustrates the effect of the control by means of the apparatusshown in FIG. 4. If this apparatus is used, the set point of the controlof the rate of feedwater supply remains at the low value h until thesalt concentration reaches the value C When this value is reached theset point of the control of the rate of feedwater supply is increased atconstant speed in d:

This increased set point remains until the salt concentration dropsbelow the value C when the set point is adjusted at constant speed untilit reaches the lower value h With this operation fluctuation of thecontrol is avoided when the salt concentrations are in the neighborhoodof the limit value C or C Switching from one set point to another isonly elfected at the predetermined limits of the salt concentration andis efliected at constant speed which is so slow that the control of thesteam generator is not disturbed.

FIG. 7 shows a modification of an apparatus according to the invention.Parts shown in FIG. 7 which correspond to parts shown in FIG. 1 aredesignated by like numerals. The system shown in FIG. 7 differs from thesystem shown in FIG. 1 in that the switching device 21 receives setpoint values for the regulator 15 from two control devices $0 and 81through signal conduits 22 and 23, respectively. The device 80 respondsto the maximum temperature sensed by the temperature sensitive devices5. The set point of the device 8%, i.e. the maximum temperature to whichit is responsive, is determined by the position of the general steamgenerator controlling device 24, the signal produced by the latter beingconducted to the device 8% through a conduit 84. The device 81 isactuated according to the average temperature measured by alltemperature sensitive devices 5 and receives its set point, i.e. theaverage temperature to which it is responsive, through a conduit 85 fromthe device 24. As in the apparatus shown in FIG. 1, the set points ofthe control of the rate of feedwater supply depend on the setting of thecontrol device 24 which corresponds to the load on or the output of thesteam generator.

At increased salt concentration the apparatus shown in FIG. 7 controlsthe rate of feedwater supply in dependence on the temperature of theoperating medium at the outlet of that one of the tube lines 4 whereinthe temperature is higher than in the outlets of the other tube lines 4,the maximum temperature being defined by a signal arriving through theconduit 84. If the salt concentration sensitive device 26 senses arelatively low salt concentration, the device 21 is switched to aposition connecting the control apparatus 15 to the regulator 81 whichresponds to the average temperature of the steam leaving the tube lines4. The average temperature which actuates the regulator 81 is defined bythe signal arriving through the conduit 8'5 and is somewhat higher thanthe maximum temperature which actuates the device 6 which maximumtemperature is that of slightly superheated steam. When the device 23.is set to transmit the set point signal pro duced in the device 81 thesteam leaving the evaporating tubes 4 is superheated and has a highertemperature than the temperature which actuates the device 80 so that nounevaporated operating medium enters the collector 6.

With the arrangement shown in FIG. 7 only so much feedwater is suppliedto the evaporator as is needed for producing the amount of steamwithdrawn from the steam generator, as long as the salt concentration isbelow a predetermined value. There is no blowdown and losses causedthereby are avoided. If the salt concentration of the operating mediumincreases above the predetermined value, the regulator 15 is connectedto the regulator 80 and the temperature of the operating medium leavingthe evaporator is so controlled that a certain percentage of operatingmedium is not evaporated and is blown down from the separator 7. If thisblowdown operation reduces the salt concentration to below thepredetermined value, the control is switched to the regulator 81 andcauses a rate of feedwater supply which is such that no unevaporatedoperating medium leaves the evaporator.

FIG. 8 shows another modification of an apparatus according to theinvention. Parts of the apparatus shown in FIG. 8 corresponding to thoseof the appartus shown in FIGS. 1 and 7 are designated by the samenumerals. The steam generator forming part of the system shown in FIG. 8has an evaporator which is split into two sections 4 and 4 which arearranged in series relation with respect to the flow of the operatingmedium. A temperature sensitive device 90 is connected to a pipeconnecting the steam space of the water separator 7 and the superheater8 and produces a signal for actuating a regulator 91 which produces aset point signal which is conducted to the switching device 21. Thelatter is also connected to a regulator 93 which is actuated by controlsignals produced by a device 14 which is responsive to the rate offeedwater supply to the steam generator. The signal produced by thedevice 14 is transformed in a conventional device 94 before it reachesthe regulator 93 so that the signal is changed, for example by a camarrangement, and the signal received by the device 93 from the device 94does not linearly correspond to the signal produced by the device 14.

A cooler 96 is interposed in the blowdown pipe of the separator 7.Downstream of the cooler 96 a valve 16 for controlling the amount ofblowdown water and a measuring device 97, 98 for measuring the rate offlow of removed blowdown water are arranged. The valve 16 is controlledby a regulator 17 to maintain a predetermined water level in theseparator 7 as in the example shown in FIG. 1. The device 98 produces asignal corresponding to the rate of flow of blowdown water which signalis transmitted to the regulator 93.

A pipe 99 with a valve 100 by-passes the separator 7. The valve 100 isoperatively connected to the salt concentration sensitive device 26 foroperation in response to the salt concentration. The valve 100 is fullyopened when the salt concentration decreases to or below a predeterminedlimit and is closed in response to an increasing salt concentration.Therefore, no water is blown down, unless the salt content of thefeedwater rises above a predetermined value.

A pipe 102 is connected to a pipe interconnecting the evaporatingsections 4 and 4' and to the pipe connecting the steam space of theseparator 7 and superheater 8, bypassing the evaporating section 4 andthe separator 7. A valve 103 and a measuring orifice plate 104 areinterposed in the pipe 102. The orifice plate 104 is connected to adevice 105 which produces a signal corresponding to the rate of flow ofoperating medium through the pipe 102. The signal produced in the device105 is conducted to a regulator 106 which actuates the valve 103. Theregulator 106 is also controlled by signals received from a signalmultiplication device 107 which multiplies signals received from theload control device 24 by signals received from the salt concentrationresponsive device 26. The load control device 24 produces a secondsignal which is transmitted to the device 91 and combined therein withthe signal produced in the temperature responsive device 90. The device91 corresponds to the device 81 in FIG. 7.

In the system according to FIG. 8 the regulator 13 controls the rate offeedwater supply to the steam generator according to a signal receivedfrom the device 91 which corresponds to the temperature of the operatingmedium and to the setting of the device 24, as long as the saltconcentration of the feedwater is relatively low. If this is the case,the valve 100 is open and no liquid is separated in the separator 7 andblown down. When the salt concentration exceeds a predetermined value,the switching device 21 connects the regulator 13 to the regulator 93 sothat the rate of feedwater supply corresponds to the relation betweenthe rate of feedwater fed into the steam gen erator and the rate ofblowdown water. If the blowdown water increases relative to the feedwater supply to the steam generator the latter is reduced so that thesteam at the outlet of the evaporator is less wet and less water isblown down. The signal ransformer 94 may determine a difierent relationbetween the rate of removed blowdown liquid and the rate of feedwatersupply at different rates of feedwater supply. For example, at lowerloads on the steam generator the rate of blowdown water may be increasedrelatively to the rate of feedwater supply for stabilizing the flowconditions through the evaporator. The multiplication device 107 and theregulator 106 effect by-passing of liquid operating medium through thepipe 102 according to the load on the steam generator and the saltconcentration in the feedwater. At high salt concentration (C in FIG. 5)the signal fed into the multiplication device 107 is zero so that thevalve 103 is closed and no operating medium is by-passed in conduit 102.At low salt concentration (C in FIG. 5) the signal fed into the device107 may have the value one and the valve 103 may be open all the way.The amount of by-passed operating medium is defined by the set pointsignal emitted from the load control device 24. This signal may be suchthat the mixture of the steam discharged by the separator 7 and thewater supplied through pipe 102 has a predetermined moisture content ortemperature. In this way changes of the moisture content and temperatureof the steam entering the superheater 8 which changes are caused bychanges of load, can be counteracted, provided that the saltconcentration of the operating medium is low. The atoredescribedarrangement reduces the normally required water injection. By openingthe valve 100 in the by-pass pipe 99 operating medium can be by-passedaround the separator 7 and'blowdown waste as well as flow resistance inthe separator 7 which causes an undesired pressure drop can be avoided.

The illustrated and described examples may be modified without departingfrom the scope of the present invention. For example, the saltconcentration responsive device 26 may be arranged at a difierent pointof the circuit of the operating medium than that shown. It may bearranged to be responsive to the entire flowing operating medium, asshown, or it may be responsive only to a portion of the operating mediumpassing through the plant. The invention is not restricted to plants inwhich the operating medium forms a closed circuit including a steamgenerator, a turbine and a condenser, but may as well be applied to asteam generator supplying consumers which do not return all or part ofthe operating medium to the steam generator. The temperature sensitivedevice in FIG. 8 need not be connected to the inlet of the superheater,as shown, but may be connected to other parts of the steam generator.

The plants shown and described by way of example are simplified andinclude only what is necessary for explaining the invention. A steamgenerating plant usually includes many additional control devices which,for example, maintain the temperature of the live steam by means ofwater injection. The load control device 24 need not necessarily be of atype which is actuated by hand, but may be responsive, for example, tothe speed of the turbine or to the pressure of the live steam enteringthe turbine. The system according to the invention may be combined withthe aforementioned additional control devices and the regulators of theillustrated and described examples may be influenced by additionalsignals for producing special effects. The regulator 15 shown in FIG. 1maybe actuated, for example, by a signal corresponding to the moisturecontent of the steam in addition to the signal which corresponds to themaximum temperature of the operating medium leaving the tubes of theevaporator 4. The regulators 15, 81 and 91 may receive signals whichcorrespond to the amount of water injected into the superheater so thatthe rate of feedvvater supply control is so adjusted that the amount ofcooling water which must be injected into the superheater remains withindesired limits. The control system according to the invention may besubjected to other influences for producing the desired result. Forexample, in the system shown in FIG. 1 an additional signal whichdepends on the salt concentration of the operating medium may be addedby a conventional signaladding device to the signal in one of theconduits 22 or 213 for changing the signal produced by the temperaturesensitive device 5.

I claim:

1. In a steam generating plant having a forced flow stem generatorincluding a tubular evaporating section, a tubular superheating section,and a water separator interposed for flow of operating medium betweensaid sections: a supply conduit connected to said evaporating sectionfor supplying feedwater thereto, a salt concentration sensitive deviceconnected to said supply conduit for sensing the salt concentration inthe feedwater and producing control signals corresponding to the sensedsalt concentration, control means connected to said supply conduit forcontrolling the rate of feedwater supply to said evaporating section,control signal transmitting means interconnecting said saltconcentration sensitive device and said control means, the latter beingadapted to be actuated by the transmitted control signals for increasingthe rate of feedwater supply upon an increase of the salt concentrationin the feedwater and for decreasing the rate of feedwater supply upon adecrease of the salt concentration in the feedwater.

2. In a steam generating plant having a forced flow steam generatorincluding a tubular evaporator section, a tubular superheating section,and a water separator interposed for flow of operating medium betweensaid sections: a supply conduit connected to said evaporating sectionfor supplying feedwater thereto, a salt concentration sensitive deviceconnected to said supply conduit for sensing the salt concentration inthe feedwater and producing control signals corresponding to the sensedsalt concentration, control means connected to said supply conduit forcontrolling the rate of feedwater supply to said evaporating section,set point adjusting signal supply means connected to said control meansfor adjusting the set point thereof, said set point adjusting signalsupply means being connected to said salt concentration sensitive devicefor increasing the set point of said control means for increasing therate of feedwater supply upon an increase of the salt concentration inthe feedwater and for decreasing the set point of said control means fordecreasing the rate of feedwater supply upon a decrease of the saltconcentration in the feedwater.

3. In a steam generating plant having a forced flow steam generatorincluding a tubular evaporating section, a tubular superheating section,and a water separator interposed for flow of operating medium betweensaid sections: a supply conduit connected to said evaporating sectionfor supplying feedwater thereto, a salt concentration sensitive deviceconnected to said supply conduit for sensing the salt concentration inthe feedwater, control means connected to said supply conduit forcontrolling the rate of feedwater supply to said evaporating section,control signal producing means individually responsive to valuescorresponding to diiferent operating conditions of the plant and adaptedto individually produce control signals corresponding to said values,signal transmitting means interconnecting said signal producing meansand said control means, and switching means interposed in said signaltransmitting means for effecting transmission of control signals fromone or from another of said signal producing means to said controlmeans, the latter being adapted to be actuated by the signalstransmitted by said transmitting means, said switching means beingoperatively connected to said salt concentration sensitive device foractuation thereby to effect transmission of control signals from one ofsaid signal producing means to said control means when the saltconcentration is at a predetermined low value and to effect transmissionof control signals from another of said signal producig means to saidcontrol means when the salt concentration is at a predetermined highvalue.

4. In a steam generating plant as defined in claim 3 and wherein saidevaporating section comprises a plurality of the tube lines arranged inparallel relation with respect to the flow of the operating mediumtherethrough, a temperature sensitive device being connected to theoutlet of each of said tube lines, one of said signal producing meansbeing operatively connected to said temperature sensitive devices andbeing adapted to produce a signal corresponding to the averagetemperature at the outlets of said tube lines, a second of said signalproducing means being operatively connected to said temperaturesensitive devices and being adapted to produce a signal corresponding tothe temperature of that one of the outlets of said tube lines which hasthe highest temperature of all outlets.

5. In a steam generating plant as defined in claim 3 and wherein one ofsaid control signal producing means is connected to said steam generatorand adapted to produce signals corresponding to the temperature of theoperating medium passing through the steam generator, a second of saidcontrol signal producing means being operatively connected to saidseparator and to said supply conduit and adapted to produce signalscorresponding to the ratio between the rate of feedwater flow to saidsteam generator and the rate of water separation in said separator.

6. In a steam generating plant having a forced flow steam generatorincluding a tubular evaporating section, a tubular superheating section,and a water separator interposed between said sections: a by-passconduit connecting said evaporating section and said superheatingsection and by-passing said separator, control means connected to saidby-pass conduit for controlling the rate of flow of operating mediumtherethrough, a supply conduit connected to said evaporating section forsupplying feedwater thereto, a salt concentration sensitive deviceconnected to said supply conduit for sensing the salt concentration inthe feedwater, control means connected to said supply conduit forcontrolling the rate of feedwater flow therethrough, said control meansbeing operatively connected to said salt concentration sensitive deviceto be actuated thereby for increasing the rate of flow of feedwaterthrough said supply conduit and for decreasing the rate of flow ofoperating medium through said by-pass conduit upon increase of the saltconcentration above a predetermined value and for decreasing the rate offeedwater flow through said supply conduit and for increasing the rateof flow of operating medium through said by-pass conduit upon decreaseof the salt concentration below a predetermined value.

7. In a steam generating plant having a forced flow steam generatorincluding a tubular evaporating section, a tubular superheating section,and a water separator interposed for flow of operating medium betweensaid sections: a supply conduit connected to said evaporating sectionfor supplying feedwater thereto, a salt concentration sensitive deviceconnected to said supply conduit for sensing the salt concentration inthe feedwater, control means connected to said supply conduit forcontrol ling the rate of feedwater flow therethrough, at least twosources of different set point adjusting signals, signal transmittingmeans connected to said sources and to said control means, and switchmeans interposed in said transmitting means for selectively transmittingsignals either from one of said sources or from another of said sourcesto said control means, said switch means being operatively connected tosaid salt concentration sensitive device for actuation thereby.

8. In a steam generating plant according to claim 7 and wherein saidswitch means is adapted to be moved to one extreme position forconnecting said control means to one of said sources upon apredetermined salt concentration sensed by said salt concentrationsensitive device and to be moved to a second extreme position forconnecting said control means to a second of said sources upon adifferent predetermined salt concentration sensed by said saltconcentration sensitive device, said switch means being adapted to bemoved to intermediate positions corresponding to salt concentrationsbetween said predetermined salt concentrations and to transmit set pointadjusting signals to said control means corresponding to values whichare between the values of the signals produced by said sources.

9. In a steam generating plant according to claim 7 and wherein one ofsaid sources supplies set point adjusting signals elfecting a relativelyhigh rate of feedwater supply and a second of said sources supplies setpoint adjusting signals efiecting a relatively low rate of feedwatersupply, actuating means for said switch means being interposed betweensaid salt concentration sensitive device and said switch means andincluding means adapted to hold said switch means in a position forconnecting said control means to said second source as long as the saltconcentration is below a predetermined relatively high value, saidactuating means including means adapted to move said switch means atsubstantially constant speed to a position for connecting said controlmeans to the first source when the salt concentration reaches saidpredetermined high value, to hold said switch means in the lastmentioned position as long as the salt concentration stays above arelatively low concentration, and to move said switch means atsubstantially constant speed for connecting said control means to saidsecond source when the salt concentration drops to said relatively lowconcentration.

10. A method of controlling the rate of feedwater supply to a forcedflow steam generator having an evaporating section, a superheatersection, and a water separator interposed in the flow of operatingmedium between said sections, comprising the steps of measuring the saltcontent of the feedwater, of increasing the rate of feedwater supply tothe steam' generator upon an increase of the salt content of thefeedwater, of decreasing the rate of feedwater supply to the steamgenerator upon a decrease of the salt content of the feedwater, and ofby-passing operating medium around the water separator upon a decreaseof the salt content of the operating medium below a predeterminedminimum.

References Cited in the file of this patent UNITED STATES PATENTS2,028,504 Eglotf June 21, 1936 2,294,501 Jenkins Sept. 1, 1942 2,962,865Buri Dec. 6, 1960 FOREIGN PATENTS 558,981 Belgium Jan. 6, 1958 693,326Great Britain June 24, 1953 771,715 Great Britain Apr. 3, 1957 1,056,147Germany Apr. 30, 1959

10. A METHOD OF CONTROLLING THE RATE OF FEEDWATER SUPPLY TO A FORCEDFLOW STEAM GENERATOR HAVING AN EVAPORATING SECTION, A SUPERHEATERSECTION, AND A WATER SEPARATOR INTERPOSED IN THE FLOW OF OPERATINGMEDIUM BETWEEN SAID SECTIONS, COMPRISING THE STEPS OF MEASURING THE SALTCONTENT OF THE FEEDWATER, OF INCREASING THE RATE OF FEEDWATER SUPPLY TOTHE STEAM GENERATOR UPON AN INCREASE OF THE SALT CONTENT OF THEFEEDWATER, OF DECREASING THE RATE OF FEEDWATER SUPPLY TO THE STEAMGENERATOR UPON A DECREASE OF THE SALT CONTENT OF THE FEEDWATER, AND OFBY-PASSING OPERATING MEDIUM AROUND THE WATER SEPARATOR UPON A DECREASEOF THE SALT CONTENT OF THE OPERATING MEDIUM BELOW A PREDETERMINEDMINIMUM.